The present invention relates to a sputtering target for producing optically transparent surface layers in combination with silvered heat reflecting layers on transparent substrates such as panes of glass and of transparent plastic. The sputtering target is formed of bismuth with 0.2 to 10% by weight manganese. In a further aspect, the present invention relates to a method of manufacturing these sputter targets and substrates produced using these novel sputtering targets.
It is known that architectural panes of glass and transparent plastic foils can be provided with thin, optically transparent layers of silver by means of coating in order to obtain a more intense reflection of heat radiation. This achieves both a protection against excessive radiation of heat into the building from the outside as well as also reduced energy losses in heated buildings due to heat radiation from the inside to the outside. Often, combinations of several layers on the glass panes are used to this end. Thus, three-layer arrangements have proven to be particularly useful which consist of a metal oxide adhesive layer, a silver layer reflecting infrared radiation and a top antireflection layer of metal oxide.
In general, the method of cathodic atomization in a glow discharge, called sputtering, is used for the manufacture of such layers. For this, the metals, metal alloys and metal oxides to be applied as layers are used as specially shaped solid-state bodies, e.g. plates, rings or also parts of a more complex geometry -- the so-called targets.
The atomization (sputtering) occurs by the process of charged gas atoms striking the target surface, as a result of which individual atoms or atom groups are dislodged from the target surface. These dislodged atoms then strike the opposing surface of the glass to be coated, where they form corresponding surface layers. The method is normally carried out in an atmosphere of noble (inert) gas, e.g. argon, under reduced pressure with applied electric voltages or high-frequency alternating currents (RF) in a direct current (DC) or high-frequency alternating current circuit.
If amounts of oxygen or nitrogen are additionally added to the noble gas atmosphere, oxide or nitride layers can also be formed, depending on the type of metal of the target. For example, adhesive oxide layers and antireflection oxide layers can be manufactured with this method using metallic targets. Usually, bismuth targets are used for this and bismuth oxide layers are applied.
It is known that pure bismuth oxide layers in direct contact with silver layers cause a blackening or darkening under UV radiation. This can be avoided if other metal oxide layers which do not cause a blackening under Uv radiation are applied between the silver layer and the bismuth oxide layers. Known examples are lead oxide, indium oxide or indium tin oxide.
German Patent No. 32 11 753 shows sputter targets for producing optically transparent surface layers of bismuth oxide which reflect heat in combination with silver layers on transparent material such as glass panes and plastic foils which consist of bismuth with 0.2 to 10% by weight manganese. However, no data is presented about the design and the manufacture of these targets.
When these known sputter targets of bismuth with 0.2 to 10% by weight manganese are used, which are manufactured by pressing and optionally by sintering an appropriate powder mixture of bismuth and manganese, manganese oxide-containing bismuth oxide layers are produced during sputtering in an oxygen-containing atmosphere of noble gas which suppress the blackening of silver layers under UV radiation. However, it has been observed that a gradual blackening of the silver layer does occur under a long-lasting action of UV radiation.